Oilpan: Fix return type of ThreadState::checkThread().

Source/platform/heap/ThreadState.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 295 matching lines @@
         return **s_threadSpecific;
 #endif
     }
 
     static ThreadState* mainThreadState()
     {
         return reinterpret_cast<ThreadState*>(s_mainThreadStateStorage);
     }
 
     bool isMainThread() const { return this == mainThreadState(); }
-    bool checkThread() const
-    {
-        ASSERT(m_thread == currentThread());
-        return true;
-    }
+    void checkThread() const { ASSERT(m_thread == currentThread()); }
 
     void didV8MajorGC(bool forceGC);
 
     void performIdleGC(double deadlineSeconds);
     void performIdleLazySweep(double deadlineSeconds);
 
     void scheduleIdleGC();
     void scheduleIdleLazySweep();
     void schedulePreciseGC();
     void scheduleGCIfNeeded();
@@ skipping 446 matching lines @@
 };
 
 template<> class ThreadStateFor<AnyThread> {
 public:
     static ThreadState* state() { return ThreadState::current(); }
 };
 
 } // namespace blink
 
 #endif // ThreadState_h